<style>
  h1,h2,h3,h4,h5,h6{
    border:1px solid red;
    width:200px;
    margin:0px;
    color:green;
  }
</style>

<h1 contenteditable="true">Heading 1</h1>
Some TEst
<h2>Heading 2</h2>
Some TEst
<h3>Heading 3</h3>
<h4>Heading 4</h4>
<h5>Heading 5</h5>
<h6>Heading 6</h6>
